Major dating sites likely still largely pull revenue from advertisement and pay-to-message hurdles.
As a photographer, however, I can attest that there is a market for people looking to pay to have a better Facebook/LinkedIn/Dating-Site profile photo.
If a good photo dramatically increases the amount of people who want to send you messages, then wouldn't subsidizing your userbase to have good photos be enormously profitable? Especially since getting just 2% of your users to take advantage of the service could make the other 98% much more likely to become paying users.
actually in Istanbul there was a studio that offered a service of making photos that look like shot in different parts of the world, partying with friends, on a sandy beach with cocktails in hand, etc. for people who otherwise never gets to be in those places and envy others on social networks that do :)
As a photographer, however, I can attest that there is a market for people looking to pay to have a better Facebook/LinkedIn/Dating-Site profile photo.